Process for the preparation of high density ethylene polymers in fluid bed reactor

ABSTRACT

A catalytic process for preparing ethylene polymers having a density of ≧0.95 to ≦0.97 and a melt flow ratio of about ≧22 to ≦32 in a low pressure gas phase process at a productivity of ≧50,000 pounds of polymer per pound of Ti with a catalyst formed from selected organoaluminum compounds and a precursor composition of the formula 
     
         Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q 
    
     wherein ED is a selected electron donor compound 
     m is ≧0.5 to ≦56 
     n is 0, 1 or 2 
     p is ≧2 to ≦116 
     q=1.5 m+2 
     R is a C 1  to C 14  aliphatic or aromatic hydrocarbon radical, or COR&#39; wherein R&#39; is a C 1  to C 14  aliphatic or aromatic hydrocarbon radical, and 
     X is selected from the group consisting of Cl, Br, I or mixtures thereof, 
     which catalyst is in particulate form and impregnated in a porous inert carrier material.

This application is a continuation of our prior U.S. application Ser.No. 12,719 filed Feb. 16, 1979 which is a continuation-in-part ofapplication 969,588 filed Dec. 14, 1978 both said applications nowabandoned.

BACKGROUND OF THE INVENTION

The invention relates to the catalytic homopolymerization andcopolymerization of ethylene with high activity Mg and Ti containingcomplex catalysts in a low pressure gas phase process to producepolymers having a density of about ≧0.95 to ≦0.97, a melt flow ratio ofabout ≧22 to ≦32 and having a relatively round particle shape and arelatively low level of fines.

DESCRIPTION OF THE PRIOR ART

Ethylene homopolymers having a density of ≧0.96 and a melt index in therange of about 5 to 50 are useful for injection molding purposesrequiring excellent impact strength properties provided that they have arelatively narrow molecular weight distribution. Ethylene polymershaving a density of ≧0.96 and a melt index of ≦20 can be made with thecatalysts and low pressure gas phase processes described in U.S. Pat.Nos. 3,023,203; 4,003,712 and 3,709,853. The polymers made with thesupported chromium oxide, silylchromate and chromocene catalysts,however, have a relatively broad molecular weight distribution asevidenced by melt flow ratio values of ≧35. The polymers of thesepatents, therefore, have relatively limited use for injection moldingapplications requiring excellent impact strength properties. It isdesirable therefore, to provide catalysts which would enable one toreadily prepare, in a gas phase process, ethylene polymers which have arelatively narrow molecular weight distribution.

To be commercially useful in a gas phase process, such as the fluid bedprocess of U.S. Pat. Nos. 3,709,853; 4,003,712 and 4,011,382, andCanadian Pat. No. 991,798 and Belgian Pat. No. 839,380, the catalystemployed must be a high activity catalyst, that is, it must have a levelof productivity of ≧50,000, preferably ≧100,000, pounds of polymer perpound of primary metal in the catalyst. This is so because such gasphase processes usually do not employ any catalyst residue removingprocedures. Thus, the catalyst residue in the polymer must be so smallthat it can be left in the polymer without causing any undue problems inthe hands of the resin fabricator and/or ultimate consumer. Low catalystresidue contents are also important where the catalyst is made withchlorine containing materials such as the titanium, magnesium and/oraluminum chlorides used in some so-called Ziegler or Ziegler-Nattacatalysts. High residual chlorine values in a molding resin will causepitting and corrosion on the metal surfaces of the molding devices. Clresidues of the order of ≧200 ppm are not commercially useful.

U.S. Pat. No. 3,989,881 discloses the use of a high activity catalystfor the manufacture, under slurry polymerization conditions, of ethylenepolymers having a relatively narrow molecular weight distribution(Mw/Mn) of about 2.7 to 3.1. Attempts were made to use catalysts similarto those described in U.S. Pat. No. 3,989,881 for the purpose of makingpolyethylene of narrow molecular weight distribution by polymerizingethylene alone or with propylene in the gas phase in a fluid bed processusing apparatus and conditions similar to those employed in U.S. Pat.No. 4,011,382 and Belgian Pat. No. 839,380. These attempts were notsuccessful. In order to avoid the use of the solvents in the slurriedcatalyst systems of U.S. Pat. No. 3,989,881, the Ti/Mg containingcomponents were dried. However, the dried material, a viscous, gummy,pyrophoric composition, could not be readily fed to the reactor becauseit was not in a free flowing form. Even when blended with silica toimprove its free-flowing properties and then added to the reactor theresults were commercially unacceptable. The productivity of the catalystwas poor, or the catalyst was pyrophoric and difficult to handle or thepolymer product was produced in the form of needleshaped products whichwere difficult to fluidize and which exhibited very poor flowproperties.

U.S. Pat. Nos. 3,922,322 and 4,035,560 disclose the use of several Tiand Mg containing catalysts for the manufacture of granular ethylenepolymers in a gas phase fluid bed process under a pressure ≦1000 psi.The use of these catalysts in these processes, however, has significantdisadvantages. The catalysts of U.S. Pat. No. 3,922,322 provide polymershaving a very high catalyst residue content, i.e., about 100 ppm of Tiand greater than about 300 ppm Cl, according to the working example ofthis patent. Further, as disclosed in the working example of U.S. Pat.No. 3,922,322, the catalyst is used in the form of a prepolymer, andvery high volumes of the catalyst composition must be fed to the reactorrelative to the volume of polymer made in the reactor. The preparationand use of this catalyst thus requires the use of relatively large sizedequipment for the manufacture, storage and transporting of the catalyst.

The catalysts of U.S. Pat. No. 4,035,560 also apparently providepolymers having high catalyst residues and the catalysts compositionsare apparently pyrophoric because of the types and amounts of reducingagents employed in such catalysts.

U.S. Pat. No. 4,124,532 discloses the polymerization of ethylene andpropylene with high activity catalysts. These catalysts comprisecomplexes which may contain magnesium and titanium. These complexes areprepared by reacting the halide MX₂ (where M may be Mg) with a compoundM'Y (where M' may be Ti and Y is halogen or an organic radical) in anelectron donor compound. These complexes are then isolated by eithercrystallization, by evaporation of the solvent or by precipitation.

Polymerization is carried out with these catalytic complexes and analkyl aluminum compound.

However, U.S. Pat. No. 4,124,532 does not disclose any specialtechniques or methods of preparing the catalyst in order to achieve thedesirable results described in the present invention. The use of thecatalysts described in U.S. Pat. No. 4,124,532, without these specialmethods, would not lead to a commercial fluid bed process to producepolyethylenes at commercial rates. In addition, the examples in the gasphase, do not describe a practical process of copolymerization toproduce copolymers with attractive polymer morphology as described inthe present invention.

U.S. Pat. No. 4,302,565 in the names of G. L. Goeke et al. and entitled"Impregnated Polymerization Catalyst, Process For Preparing, and Use forEthylene Copolymerization" discloses that ethylene copolymers, having adensity of about ≧0.91 to ≦0.94 and a melt flow ratio of ≧22 to ≦32 andwhich have relatively low residual catalyst content and a relativelyhigh bulk density and which provide films of good clarity can beproduced at relatively high productivities for commercial purposes by agas phase process if the ethylene is copolymerized with one or more C₃to C₆ alpha olefins in the presence of a high activitymagnesium-titanium containing complex catalyst prepared under specificactivation conditions with an organoaluminum compound and impregnated ina porous inert carrier material.

In the catalyst activation procedure the activation is conducted in atleast two stages. In the first stage the precursor composition,impregnated in the silica, is reacted with, and partially activated by,enough activator compound so as to provide a partially activatedprecursor composition which has an activator compound/Ti molar ratio ofabout >0 to <10:1 and preferably of about 4 to 8:1. In order to renderthe partially activated and impregnated precursor composition active forethylene polymerization purposes, additional activator compound mustalso be added to the polymerization reactor to complete, in the reactor,the activation of the precursor composition. The additional activatorcompound and the partially activated impregnated precursor compositionare preferably fed to the reactor through separate feed lines. Theadditional activator compound may be sprayed into the reactor in theform of a solution thereof in a hydrocarbon solvent such as isopentane,hexane, or mineral oil. This solution usually contains about 2 to 30weight percent of the activator compound.

However, the activity of the impregnated catalysts as prepared accordingto the procedure as described in U.S. Pat. No. 4,302,565 is at times nothigh enough to produce ethylene homopolymers or copolymers of high meltindex (≧1.0) with a density ≧0.95 and obtain a relatively round particleshape and a relatively low level of fines. Precursor compositions inwhich q=1.5 m+2 (see below) when activated in a two stage processexhibited lower polymerization activity (Table III).

U.S. patent application Ser. No. 892,037 filed on Mar. 31, 1978 in thenames of B. E. Wagner et al. and entitled Polymerization Catalyst,Process For Preparing And, Use For Ethylene Homopolymerization, nowabandoned, and continuation-in-part application Ser. No. 014,412, filedFeb. 27, 1979 disclose that ethylene homopolymers having a density rangeof 0.96 to 0.97 and a melt flow ratio of ≧22 to ≦32 and which have arelatively low residual catalyst residue can be produced at relativelyhigh productivities for commercial purposes by a low pressure gas phaseprocess if the ethylene is homopolymerized in the presence of a highactivity magnesium-titanium complex catalyst blended with an inertcarrier material. However, the polymers produced with this blendedcatalyst have the disadvantage that the polymer particles formed duringthe fluid bed polymerization process are irregular in shape and aresomewhat difficult to fluidize. Also, the final product contains arelatively high level of fines, i.e., particles having a particle sizeof ≦125 microns.

SUMMARY OF THE INVENTION

It has now been unexpectedly found that ethylene homopolymers andcopolymers having a density range of about ≧0.95 to ≦0.97 and a meltflow ratio of about ≧22 to ≦32 can be produced at relatively highproductivities at a relatively high bulk density, with relatively lowlevel of fines and with a relatively round particle shape. Thesepolymers can be produced commercially by a low pressure gas phaseprocess if the ethylene is homopolymerized or copolymerized in thepresence of a high activity magnesium-titanium complex catalyst preparedas described below, and impregnated in selected amounts in a porousinert carrier material and activated under specific conditions in thepolymerization reactor.

An object of the present invention is to provide a process forproducing, with relatively high productivities and in a low pressure gasphase process, ethylene homopolymers and copolymers which have a densityof about ≧0.95 to ≦0.97, a melt flow ratio of about ≧22 to ≦32, arelatively low residual catalyst content and a bulk density of about 21to 32 pounds per cubic foot.

Another object of the present invention is to provide granular ethylenepolymers which have a particle shape which is round and wherein thefinal polymer product contains a relatively low level of fines(particles ≧125 microns).

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows a gas phase fluid bed reactor system in which thecatalyst system of the present invention may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It has now been found that the desired ethylene homopolymers andcopolymers having a density of about ≧0.95 to ≦0.97, a low melt flowratio and relatively high bulk density values can be readily producedwith relatively high productivities in a low pressure gas phase fluidbed reaction process if the monomer charge is polymerized under aspecific set of operating conditions, as detailed below, and in thepresence of a specific high activity catalyst, which is impregnated inan inert porous carrier material in order to achieve high activity andimproved polymer particle morphology (including a relatively low levelof fines) in producing ethylene polymers. Additionally, elimination ofthe activation of the precursor composition (where q=1.5 m+2; see below)impregnated in the carrier prior to charging it to a reactor, asdescribed in U.S. Pat. No. 4,302,565, provides for the high activity ofthe catalyst and at the same time the improved polymer particlemorphology of the resulting ethylene polymers.

The Ethylene Polymers

The ethylene polymers have a melt flow ratio of about ≧22 to ≦32, andpreferably of ≧25 to ≦30. The melt flow ratio value is another means ofindicating the molecular weight distribution of a polymer. The melt flowratio (MFR) range of ≧22 to ≦32 thus corresponds to a Mw/Mn value rangeof about 2.7 to 4.1 and the MFR range of ≧25 to ≦30 corresponds to aMw/Mn range of about 2.8 to 3.6.

The copolymers which may be prepared in the process of the presentinvention are copolymers of a major mol percent (≧98%) of ethylene, anda minor mol percent (≦2%) of one (copolymer) or more (ter-,tetrapolymers) C₃ to C₈ alpha olefins. The C₃ to C₈ alpha olefins shouldnot contain any branching on any of their carbon atoms which is closerthan the fourth carbon atom.

These alpha olefins include propylene, butene-1 pentene-1, hexene-1,4-methyl pentene-1, heptene-1 and octene-1. The preferred alpha olefinsare propylene, butene-1, hexene-1, 4-methyl pentene-1 and octene-1.

The ethylene polymers have a density of about ;24 0.95 to ≦0.97,preferably from about 0.955 to 0.970. The density of the copolymer, at agiven melt index level for the copolymer, is primarily regulated by theamount of the C₃ to C₈ comonomer which is copolymerized with theethylene. In the absence of the comonomer, the ethylene wouldhomopolymerize with the catalyst of the present invention to providehomopolymers having a density of about ≧0.96. Thus, the addition ofprogressively larger amounts of the comonomers to the copolymers resultsin a progressive lowering of the density of the copolymer. The amount ofeach of the various C₃ to C₈ comonomers needed to achieve the sameresult will vary from comonomer to comonomer, under the same conditions.

Thus, to achieve the same results, in the copolymers, in terms of agiven density, at a given melt index level, larger molar amounts of thedifferent comonomers would be needed in the order of C₃ >C₄ >C₅ >C₆ >C₇>C₈.

The melt index of a homopolymer or copolymer is a reflection of itsmolecular weight. Polymers having a relatively high molecular weight,have a relatively low melt index. Ultra-high molecular weight ethylenepolymers have a high load (HLMI) melt index of about 0.0 and very highmolecular weight ethylene polymers have a high load melt index (HLMI) ofabout 0.0 to about 1.0. Such high molecular weight polymers aredifficult, if not impossible, to mold in conventional injection moldingequipment. The polymers made in the process of the present invention, onthe other hand, can be readily molded, in such equipment. They have astandard or normal load melt index of ≧0.0 to about 100, and preferablyof about 0.5 to 80, and a high load melt index (HLMI) of about 11 toabout 2000. The melt index of the polymers which are made in the processof the present invention is a function of a combination of thepolymerization temperature of the reaction, the density of the copolymerand the hydrogen/monomer ratio in the reaction system. Thus, the meltindex is raised by increasing the polymerization temperature and/or bydecreasing the density of the polymer and/or by increasing thehydrogen/monomer ratio. In addition to hydrogen other chain transferagents such as dialkyl zinc compounds may also be used to furtherincrease the melt index of the polymers.

The polymers of the present invention have an unsaturated group contentof ≦1, and usually ≧0.1 to ≦0.3, C=C/1000 carbon atoms, and acyclohexane extractables content of less than about 3, and preferablyless than about 2, weight percent.

The polymers of the present invention have a residual catalyst content,in terms of parts per million of titanium metal, of less than 20 partsper million, (ppm) at a productivity level of ≧50,000. In terms of Cl,Br or I residues, the polymers of the present invention typically have aresidue content (Cl, Br or I/Ti=7) of less than about 140 ppm at aproductivity of ≧50,000.

The polymers of the present invention are granular materials which havean average particle size of the order of about 0.02 to about 0.05inches, and preferably of about 0.02 to about 0.04 inches, in diameter.The particle size is important for the purposes of readily fluidizingthe polymer particles in the fluid bed reactor, as described below.These granular materials also have a low level of fines (≦4.0 percent ofthe total polymer product) and these fines are ≦125 microns. Also, thesegranular materials exhibit a much more spherical shape (as observed byoptical microscopy) than the granular materials described in U.S. Pat.application Ser. Nos. 892,037 and 014,412, supra.

The polymers of the present invention have a bulk density of about 21 to32 pounds per cubic foot.

High Activity Catalyst

The compounds used to form the high activity catalyst used in thepresent invention comprise at least one titanium compound, at least onemagnesium compound, at least one electron donor compound, at least oneactivator compound and at least one inert carrier material, as definedbelow.

The titanium compound has the structure

    Ti(OR).sub.a X.sub.b

wherein R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, orCOR' where R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical,

X is selected from the group consisting of Cl, Br I, or mixturesthereof, a is 0, 1 or 2, b is 1 to 4 inclusive and a+b=3 or 4.

The titanium compounds can be used individually or in combinationsthereof, and would include TiCl₃, TiCl₄, Ti(OC₆ H₅)Cl₃, Ti(OCOCH₃)Cl₃and Ti(OCOC₆ H₅)Cl₃.

The magnesium compound has the structure

    MgX.sub.2

wherein X is selected from the group consisting of Cl, Br, I, ormixtures thereof. Such magnesium compounds can be used individually orin combinations thereof and would include MgCl₂ MgBr₂ and MgI₂.Anhydrous MgCl₂ is the particularly preferred magnesium compound.

About 0.5 to 56, and preferably about 1 to 10 moles of the magnesiumcompound are used per mol of the titanium compound in preparing thecatalysts employed in the present invention.

The titanium compound and the magnesium compound should be used in aform which will facilitate their dissolution in the electron donorcompound, as described herein below.

The electron donor compound is an organic compound which is liquid at25° C. and in which the titanium compound and the magnesium compound arepartially or completely soluble. The electron donor compounds are known,as such, or as Lewis bases.

The electron donor compounds would include such compounds as alkylesters of aliphatic and aromatic carboxylic acids, aliphatic ethers,cyclic ethers and aliphatic ketones. Among these electron donorcompounds the preferable ones are alkyl esters of C₁ to C₄ saturatedaliphatic carboxylic acids; alkyl esters of C₇ to C₈ aromatic carboxylicacids; C₂ to C₈, and preferably C₃ to C₄, aliphatic ethers; C₃ to C₄cyclic ethers, and preferably C₄ cyclic mono- or di-ether; C₃ to C₆, andpreferably C₃ to C₄, aliphatic ketones. The most preferred of theseelectron donor compounds would include methyl formate, ethyl acetate,butyl acetate, ethyl ether, hexyl ether, tetrahydrofuran, dioxane,acetone and methyl isobutyl ketone.

The electron donor compounds can be used individually or in combinationsthereof.

The activator compound has the structure

    AlR.sub.3

wherein the R's are the same or different and are C₁ to C₁₄ saturatedhydrocarbon radicals.

Such activator compounds can be used individually or in combinationsthereof and would include Al(C₂ H₅)₃, Al(i-C₄ H₉)₃, and Al(C₆ H₁₃)₃.

About 10 to 400, and preferably about 15 to 60 mols of the activatorcompound are used per mol of the titanium compound in activating thecatalysts employed in the present invention.

The carrier materials are solid, particulate porous materials which areinert to the other components of the catalyst composition, and to theother active components of the reaction system. These carrier materialswould include inorganic materials such as oxides of silicon and/oraluminum. The carrier materials are used in the form of dry powdershaving an average particle size of about 10 to 250, and preferably ofabout 50 to 150 microns. These materials are also porous and have asurface area of ≧3, and preferably of ≧50, square meters per gram.Catalyst activity or productivity is apparently also improved withsilica having pore sizes of ≧80 Angstrom units and preferably of ≧100Angstrom units. The carrier material should be dry, that is, free ofabsorbed water. Drying of the carrier material is carried out by heatingit at a temperature of ≧600° C. Alternatively, the carrier materialdried at a temperature of ≧200° C. may be treated with about 1 to 8weight percent of one or more of the aluminum alkyl compounds describedabove. This modification of the support by the aluminum alkyl compoundsprovides the catalyst composition with increased activity and alsoimproves polymer particle morphology of the resulting ethylene polymers.

Catalyst Preparation: Formation of Precursor

The catalyst in the present invention is prepared by first preparing aprecursor composition from the titanium compound, the magnesiumcompound, and the electron donor compound, as described below, and thenimpregnating the carrier material with the precursor composition.

The precursor composition is formed by dissolving the titanium compoundand the magnesium compound in the electron donor compound at atemperature of about 20° C. up to the boiling point of the electrondonor compound. The titanium compound can be added to the electron donorcompound before or after the addition of the magnesium compound, orconcurrent therewith. The dissolution of the titanium compound and themagnesium compound can be facilitated by stirring, and in some instancesby refluxing these two compounds in the electron donor compound. Afterthe titanium compound and the magnesium compound are dissolved, theprecursor composition may be isolated by crystallization or byprecipitation with a C₅ to C₈ aliphatic or aromatic hydrocarbon such ashexane, isopentane or benzene.

The crystallized or precipitated precursor composition may be isolated,in the form of fine, free flowing particles having an average particlesize of about 10 to 100 microns and a settled bulk density of about 18to 33 pounds per cubic foot.

Catalyst Preparation Impregnation of Precursor in the Support

The precursor composition is then impregnated, in a weight ratio ofabout 0.033 to 1, and preferably about 0.1 to 0.43, parts of theprecursor composition into one part by weight of the carrier material.

The impregnation of the dried (activated) support with the precursorcomposition may be accomplished by dissolving the precursor compositionin the electron donor compound, and by then admixing the support withthe dissolved precursor composition so as to allow the precursorcomposition to impregnate the support. The solvent is then removed bydrying at temperatures of ≦70° C.

The support may also be impregnated with the precursor composition byadding the support to a solution of the chemical raw materials used toform the precursor composition in the electron donor compound, withoutisolating the precursor composition from such solution. This representsthe preferred method because of its simplicity. The excess electrondonor compound is then removed by drying at a temperature of ≦70° C.

In the drying process it is necessary to control the level of theelectron donor [ED]_(q) to such an extent that the final value of q=1.5m+2. This procedure involves careful drying of the precursor andconsiderable care must be exercised to avoid overdrying and hencedecomposition of the precursor.

When thus made as disclosed above the impregnated precursor compositionhas a formula

    Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q

Wherein ED is the electron donor compound.

m is ≧0.5 to ≦56, and preferably ≧1.5 to ≦5,

n is 0, 1 or 2,

p is ≧2 to ≦116, and preferably ≧6 to ≦14,

q=1.5 m+2

R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, or COR'wherein R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical and,

X is selected from the group consisting of Cl, Br, I or mixturesthereof.

The subscript for the element titanium (Ti) is the arabic numeral one.

Activation of the Impregnated Precursor Composition

In order to render the impregnated precursor composition active forethylene polymerization purposes, activator compound is added to thepolymerization reactor to activate the precursor composition. Theactivator compound and the impregnated precursor composition arepreferably fed to the reactor through separate feed lines. The activatorcompound may be sprayed into the reactor in the form of a solutionthereof in a hydrocarbon solvent such as isopentane, hexane, or mineraloil. This solution usually contains about 2 to 30 weight percent of theactivator compound. The activator compound is added to the reactor insuch amounts as to provide a total Al/Ti molar ratio of 10 to 400 andpreferably of about 15 to 60. The activator compound added to thereactor, reacts with, and activates the titanium compound in thereactor.

In a continuous gas phase process, such as the fluid bar processdisclosed below, discrete portions of the precursor compositionimpregnated on the support are continuously fed to the reactor, withdiscrete portions of activator compound needed to activate the precursorcomposition, during the continuing polymerization process in order toreplace active catalyst sites that are expended during the course of thereaction.

The Polymerization Reaction

The polymerization reaction is conducted by contacting a stream of themonomer(s), in a gas phase process, such as in the fluid bed processdescribed below, and substantially in the absence of catalyst poisonssuch as moisture, oxygen, carbon monoxide, carbon dioxide and acetylene,with a catalytically effective amount of the completely activatedprecursor composition (the catalyst) impregnated on a support at atemperature and at a pressure sufficient to initiate the polymerizationreaction.

A fluidized bed reaction system which can be used in the practice of theprocess of the present invention is illustrated in FIG. 1. Withreference thereto the reactor 10 consists of a reaction zone 12 and avelocity reduction zone 14.

The reaction zone 12 comprises a bed of growing polymer particles,formed polymer particles and a minor amount of catalyst particlesfluidized by the continuous flow of polymerizable and modifying gaseouscomponents in the form of make-up feed and recycle gas through thereaction zone. To maintain a viable fluidized bed, the mass gas flowrate through the bed must be above the minimum flow required forfluidization, and preferably from about 1.5 to about 10 times G_(mf) andmore preferably from about 3 to about 6 times G_(mf). G_(mf) is used inthe accepted form as the abbreviation for the minimum mass gas flowrequired to achieve fluidization, C. Y. Wen and Y. H. Yu, "Mechanics ofFluidization", Chemical Engineering Progress Symposium Series, Vol. 62,p. 100-111 (1966).

It is essential that the bed always contains particles to prevent theformation of localized "hot spots" and to entrap and distribute theparticulate catalyst throughout the reaction zone. On start up, thereactor is usually charged with a base of particulate polymer particlesbefore gas flow is initiated. Such particles may be identical in natureto the polymer to be formed or different therefrom. When different, theyare withdrawn with the desired formed polymer particles as the firstproduct. Eventually, a fluidized bed of the desired polymer particlessupplants the start-up bed.

The impregnated precursor composition used in the fluidized bed ispreferably stored for service in a reservoir 32 under a blanket of a gaswhich is inert to the stored material, such as nitrogen or argon.

Fluidization is achieved by a high rate of gas recycle to and throughthe bed, typically in the order of about 50 times the rate of feed ofmake-up gas. The fluidized bed has the general appearance of a densemass of viable particles in possible free-vortex flow as created by thepercolation of gas through the bed. The pressure drop through the bed isequal to or slightly greater than the mass of the bed divided by thecross-sectional area. It is thus dependent on the geometry of thereactor.

Make-up gas is fed to the bed at a rate equal to the rate at whichparticulate polymer product is withdrawn. The composition of the make-upgas is determined by a gas analyzer 16 positioned above the bed. The gasanalyzer determines the composition of the gas being recycled and thecomposition of the make-up gas is adjusted accordingly to maintain anessentially steady state gaseous composition within the reaction zone.

To insure complete fluidization, the recycle gas and, where desired,part of the make-up gas are returned to the reactor at point 18 belowthe bed. There exists a gas distribution plate 20 above the point ofreturn to aid fluidizing the bed.

The portion of the gas stream which does not react in the bedconstitutes the recycle gas which is removed from the polymerizationzone, preferably by passing it into a velocity reduction zone 14 abovethe bed where entrained particles are given an opportunity to drop backinto the bed. Particle return may be aided by a cyclone 22 which may bepart of the velocity reduction zone or exterior thereto. Where desired,the recycle gas may then be passed through a filter 24 designed toremove small particles at high gas flow rates to prevent dust fromcontacting heat transfer surfaces and compressor blades.

The recycle gas is then compressed in a compressor 25 and then passedthrough a heat exchanger 26 wherein it is stripped of heat of reactionbefore it is returned to the bed. By constantly removing heat ofreaction, no noticeable temperature gradient appears to exist within theupper portion of the bed. A temperature gradient will exist in thebottom of the bed in a layer of about 6 to 12 inches, between thetemperature of the inlet gas and the temperature of the remainder of thebed. Thus, it has been observed that the bed acts to almost immediatelyadjust the temperature of the recycle gas above this bottom layer of thebed zone to make it conform to the temperature of the remainder of thebed thereby maintaining itself at an essentially constant temperatureunder steady conditions. The recycle is then returned to the reactor atits base 18 and to the fluidized bed through distribution plate 20. Thecompressor 25 can also be placed upstream of the heat exchanger 26.

The distribution plate 20 plays an important role in the operation ofthe reactor. The fluidized bed contains growing and formed particulatepolymer particles as well as catalyst particles. As the polymerparticles are hot and possibly active, they must be prevented fromsettling, for if a quiescent mass is allowed to exist, any activecatalyst contained therein may continue to react and cause fusion.Diffusing recycle gas through the bed at a rate sufficient to maintainfluidization at the base of the bed is, therefore, important. Thedistribution plate 20 serves this purpose and may be a screen, slottedplate, perforated plate, a plate of the bubble cap type and the like.The elements of the plate may all be stationary, or the plate may be ofthe mobile type disclosed in U.S. Pat. No. 3,298,792. Whatever itsdesign, it must diffuse the recycle gas through the particles at thebase of the bed to keep them in a fluidized condition, and also serve tosupport a quiescent bed of resin particles when the reactor is not inoperation. The mobile elements of the plate may be used to dislodge anypolymer particles entrapped in or on the plate.

Hydrogen may be used as a chain transfer agent in the polymerizationreaction of the present invention. The ratio of hydrogen/ethyleneemployed will vary between about 0 to about 2.0 moles of hydrogen permole of the monomer in the gas stream.

Any gas inert to the catalyst and reactants can also be present in thegas stream. The activator compound is preferably added to the gasrecycle system at the hottest portion thereof. Addition into the recycleline, therefore, downstream from the heat exchanger is preferred, asfrom dispenser 27 thru line 27A.

Compounds of the structure Zn(R_(a))(R_(b)), wherein R_(a) and R_(b) arethe same or different C₁ to C₁₄ aliphatic or aromatic hydrocarbonradicals, may be used in conjunction with hydrogen, with the catalystsof the present invention as molecular weight control or chain transferagents, that is, to increase the melt index values of the copolymersthat are produced. About 0 to 50, and preferably about 20 to 30 moles ofthe Zn compound (as Zn) would be used in the gas stream in the reactorper mol of titanium compound (as Ti) in the reactor. The zinc compoundwould be introduced into the reactor preferably in the form of a dilutesolution (2 to 10 weight percent) in a hydrocarbon solvent or absorbedon a solid diluent material, such as silica, in amounts of about 10 to50 weight percent. These compositions tend to be pyrophoric. The zinccompound may be added into the recycle gas stream from a feeder adjacentto feeder 27.

It is essential to operate the fluid bed reactor at a temperature belowthe sintering temperature of the polymer particles. To insure thatsintering will not occur, operating temperatures below the sinteringtemperature are desired. For the production of ethylene polymers in theprocess of the present invention an operating temperature of about 90°to 105° C. is preferably used to prepare products having a density ofabout 0.95 to 0.97.

The fluid bed reactor is operated at pressures of up to about 1000 psi,and is preferably operated at a pressure of from about 150 to 350 psi,with operation at the higher pressures in such ranges favoring heattransfer since an increase in pressure increases the unit volume heatcapacity of the gas.

The impregnated precursor composition is injected into the bed at a rateequal to its consumption at a point 30 which is above the distributionplate 20. A gas which is inert to the impregnated precursor compositionsuch as nitrogen or argon is used to carry the composition into the bed.Injecting the precursor composition at a point above the distributionplate is an important feature of this invention. Since the catalystsformed from the impregnated precursor composition used in the practiceof the invention are highly active, injection into the area below thedistribution plate may cause polymerization to begin there andeventually cause plugging of the distribution plate. Injection into theviable bed, instead, aids in distributing the catalyst throughout thebed and tends to preclude the formation of localized spots of highcatalyst concentration which may result in the formation of "hot spots".

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at a rate equal to the rate of formation of theparticulate polymer product. Since the rate of heat generation isdirectly related to product formation, a measurement of the temperaturerise of the gas across the reactor (the difference between inlet gastemperature and exit gas temperature) is determinative of the rate ofparticulate polymer formation at a constant gas velocity.

The particulate polymer product is preferably continuously withdrawn ata point 34 at or close to the distribution plate 20 and in suspensionwith a portion of the gas stream which is vented before the particlessettle to preclude further polymerization and sintering when theparticles reach the ultimate collection zone. The suspending gas mayalso be used, as mentioned above, to drive the product of one reactor toanother reactor.

The particulate polymer product is conveniently and preferably withdrawnthrough the sequential operation of a pair of timed valves 36 and 38defining a segregation zone 40. While valve 38 is closed, valve 36 isopened to emit a plug of gas and product to the zone 40 between it andvalve 36 which is then closed. Valve 38 is then opened to deliver theproduct to an external recovery zone. Valve 38 is then closed to awaitthe next product recovery operation.

Finally, the fluidized bed reactor is equipped with an adequate ventingsystem to allow venting the bed during the start up and shut down. Thereactor does not require the use of stirring means and/or wall scrapingmeans.

The highly active supported catalyst system of this invention appears toyield a fluid bed product having an average particle size between about0.02 to about 0.05 inches and preferably about 0.02 to about 0.04 incheswherein catalyst residue is unusually low. The polymer particles have arelatively round particle shape and a relatively low level of fines(<125 microns) i.e., ≦4 percent by weight.

The feed stream of gaseous monomer, with or without inert gaseousdiluents, is fed into the reactor to achieve a space time yield of about2 to 10 pounds/hour/cubic foot of bed volume.

The term virgin resin or polymer as used herein means polymer, ingranular form, as it is recovered from the polymerization reactor.

The following Examples are designed to illustrate the process of thepresent invention and are not intended as a limitation upon the scopethereof.

The properties of the polymers produced in the Examples were determinedby the following test methods:

    ______________________________________                                        Density       A plaque is made and conditioned                                              for one hour at 120° C. to approach                                    equilibrium crystallinity and is                                              then quickly cooled to room temper-                                           ature. Measurement for density is                                             then made in a density gradient                                               column.                                                         Melt Index (MI)                                                                             ASTM D-1238 - Condition E --                                                  Measured at 190° C. - reported                                         as grams per 10 minutes.                                        Flow Rate (HLMI)                                                                            ASTM D-1238 - Condition F --                                                  Measured at 10 times the weight                                               used in the melt index test above.                               ##STR1##                                                                     Productivity  A sample of the resin product                                                 is ashed, and the weight percent                                              of ash is determined; since                                                   the ash is essentially                                                        composed of the catalyst, the                                                 productivity is thus the                                                      pounds of polymer produced per                                                pound of total catalyst                                                       consumed. The amount of Ti,                                                   Mg and Cl in the ash are                                                      determined by elemental                                                       analysis.                                                       Bulk Density  The resin is poured via 3/8"                                                  diameter funnel into a 100 ml                                                 graduated cylinder to 100 ml                                                  line without shaking the                                                      cylinder, and weighed by                                                      difference.                                                     Average Particle Size                                                                       This is calculated from sieve                                                 analysis data measured according to                                           ASTM-D-1921 Method A using a 500 g.                                           sample. Calculations are based on                                             weight fractions retained on the                                              screens.                                                        ______________________________________                                    

IA. PREPARATION OF IMPREGNATED PRECURSOR

In a 12 liter flask equipped with a mechanical stirrer are placed 41.8 g(0.439 mol) anhydrous MgCl₂ and 2.5 l tetrahydrofuran (THF). To thismixture, 27.7 g (0.184 mol) TiCl₄ is added dropwise over 1/2 hour. Itmay be necessary to heat the mixture to 60° C. for about 1/2 hour inorder to completely dissolve the material.

The precursor composition may be isolated by recovering it from thesolution in THF by crystallization or precipitation. It may also beanalyzed at this point for Mg and Ti content since some of the Mg and/orTi compound may have been lost during the isolation of the precursorcomposition.

The empirical formulas used herein in reporting the precursorcompositions are derived by assuming that the Mg and the Ti still existin the form of the compounds in which they were first added to theelectron donor compound. The amount of electron donor is determined bychromatography.

The impregnated precursor composition is prepared by adding 500 g ofporous silica, dehydrated at 800° C., optionally treated with 4 to 8wt.% triethyl aluminum to the solution prepared above and the mixture isstirred for 1/4 hour. The mixture is dried with a N₂ purge at 60° C. forabout 3-5 hours to provide a dry free flowing powder having the particlesize of the silica. The absorbed precursor composition has the formula:

    TiMg.sub.3.0 Cl.sub.10 (THF).sub.6.7

[In this formula the calculated value of q is 6.5 in excellent agreementwith the 6.7 value measured experimentally.]

This procedure can be used to prepare the impregnated precursor onsilica treated with triethyl aluminum. Silica, previously dehydrated at800° C. is treated with triethyl aluminum to produce a silica modifiedwith 4 weight percent triethyl aluminum.

IB. PREPARATION OF IMPREGNATED PRECURSOR FROM PREFORMED PRECURSORCOMPOSITION

In a 12 liter flask equipped with a mechanical stirrer, 146 g ofprecursor composition is dissolved in 2.5 liters dry THF. The solutionmay be heated to 60° C. in order to facilitate dissolution. 500 g ofporous silica, dehydrated at 800° C., is added and the mixture isstirred for 1/4 hour. The mixture is dried with a N₂ purge at ≦60° C.for about 3-5 hours to provide a dry free flowing powder having theparticle size of the silica.

II. ACTIVATION PROCEDURE

The activator compound is fed to the polymerization reactor for thepurpose of activating the precursor composition. It is fed into thereactor as a dilute solution in a hydrocarbon solvent such asisopentane. These dilute solutions contain about 5 to 30% by volume ofthe activator compound.

The activator compound is added to the polymerization reactor so as tomaintain the Al/Ti ratio in the reactor at a level of about ≧10 to 400:1and preferably of 15 to 60:1.

EXAMPLES 1 TO 6

Ethylene was homopolymerized in each of this series of Examples withcatalyst formed as described above. The silica impregnated precursorcomposition contained 20 to 35 percent by weight (percent loading) ofprecursor composition. The activation of the precursor composition inthe polymerization reactor was accomplished with triethyl aluminum in afive weight percent isopentane solution so as to provide the activatedcatalyst in the reactor with an Al/Ti mol ratio of 15-40.

Each of the polymerization reactions was continuously conducted for >1hour after equilibrium was reached and under a pressure of about 300psig and a gas velocity of 3 to 4 times G_(mf) in a fluid bed reactorsystem at a space time yield of about 3 to 6 lbs/hr/ft³ of bed space.The reaction system was as described in the drawing above. It has alower section 10 feet high and 131/2 inches in (inner) diameter, and anupper section which is 16 feet high and 231/2 inches in (inner)diameter.

Table I below lists the percent loading of the precursor composition,type of silica, reaction temperature, H₂ /C₂ mol ratio as well as meltindex, melt flow ratio, density, residual titanium, average particlesize, bulk density, and fines of the granular virgin resins made inthese Examples.

                                      TABLE I                                     __________________________________________________________________________    Reaction Conditions Using Catalyst of the Present Invention                                                                             Fines               Ex-                                                                              Percent Loading of                                                                      Silica treated                Residual                                                                           Average                                                                            Bulk <125                am-                                                                              the Precursor                                                                           with triethyl                                                                          Temp.                                                                             H.sub.2 /C.sub.2                                                                  MI      Density                                                                            Ti   Particle                                                                           Density                                                                            microns             ple                                                                              Composition                                                                             aluminum (wt. %)                                                                       (°C.)                                                                      Ratio                                                                             dg/min                                                                            MFR g/cc ppm  Size, in.                                                                          lbs/ft.sup.3                                                                       wt.                 __________________________________________________________________________                                                              %                   1  20        Yes (8)   95 0.56                                                                              13  26  0.970                                                                              10   0.031                                                                              28   1.6                 2  20        Yes (8)  105 0.37                                                                              9.3 24  0.970                                                                               9   0.030                                                                              26   1.6                 3  25        Yes (4)  103 0.38                                                                              6.8 25  0.968                                                                               5   0.024                                                                              25   3.5                 4  30        Yes (4)  103 0.45                                                                              8.4 26  0.969                                                                               7   0.026                                                                              26   3.8                 5  30        No       103 0.42                                                                              9.9 25  0.970                                                                              12   0.031                                                                              22   2.2                 6  35        Yes (4)  103 0.42                                                                              9.2 28  0.970                                                                              17   0.037                                                                              22   1.2                 __________________________________________________________________________

COMPARATIVE EXAMPLES A AND B

A catalyst was prepared according to the procedure as found in U.S. Pat.application Ser. Nos. 892,037 014,412, supra, as follows:

III. PREPARATION OF PRECURSOR COMPOSITION

In a 5 liter flask equipped with a mechanical stirrer, 16.0 g (0.168Mol) of anhydrous MgCl₂ was mixed with 850 ml of pure tetrahydrofuranunder nitrogen. The mixture was stirred at room temperature (˜25° C.)while 13.05 g (0.069 Mol) of TiCl₄ was added dropwise. After completeaddition, the contents of the flask were heated to reflux for about 1/2to 1 hour to dissolve the solids. The system was cooled to roomtemperature and 3 liters of pure n-hexane was slowly added over a periodof 1/4 hour. A yellow solid precipitated. The supernatant was decantedand the solids were washed with 3X one liter of n-hexane. The solidswere filtered and dried in a rotating evaporating flask at 40°-60° C. togive 55 g of solid precursor composition.

IV. Activation Procedure

The activation is conducted in such a way that the precursor compositionis only partially activated prior to the introduction thereof into thepolymerization reactor, and then the remainder of the activation processis completed within such reactor.

400 grams of silica is charged to a mixing vessel or tank. The silica isthen admixed with sufficient amounts of isopentane to provide a slurrysystem. This usually requires about 4 to 7 ml of diluent per gram ofinert carrier. 100 g. of the precursor composition is then charged tothe mixing vessel and thoroughly admixed with the slurry composition.The precursor composition has an elemental titanium content of 1±0.1millimole of Ti per gram of precursor composition. About 5.0 equivalentof triethyl aluminum is added to the contents of the mixing vessel so asto partially activate the precursor composition. The triethyl aluminumis added to the mixing vessel in the form of a solution which contains20 weight percent of the triethyl aluminum in hexane. The activation isaccomplished by thoroughly mixing and contacting the triethyl aluminumcompound with the precursor composition. All of the operations describedabove are conducted at room temperature, and at atmospheric pressure inan inert atmosphere.

The resulting slurry is then dried under a purge of dry inert gas suchas nitrogen or argon, at atmospheric pressure at a temperature of ≦60°C. to remove the hydrocarbon diluent. This process usually requiresabout 3 to 5 hours. The resulting product is in the form of a dryfree-flowing particulate material wherein the activated precursorcomposition is uniformly blended with the inert carrier. The driednon-pyrophoric product is stored under an inert gas.

The partially activated precursor composition is fed to thepolymerization reactor and completely activated in the reactor by theactivator compound. The activator compound is fed into the reactor as adilute solution in a hydrocarbon solvent such as isopentane. Thesedilute solutions contain about 5 to 30% by volume of the activatorcompound.

The activator compound is added to the polymerization reactor so as tomaintain the Al/Ti ratio in the reactor at a level of about 10 to 400:1and preferably of 15 to 60:1.

Ethylene was homopolymerized with catalyst formed as described inprocedure I and II, of the present invention, and also with catalystformed as described in procedure III and IV, as found in Ser. Nos.892,037 014,412. The silica impregnated precursor composition formed byprocedure I and II contained 20 percent by weight of precursorcomposition. This precursor composition as well as the partiallyactivated precursor composition formed in procedure III and IV wereactivated in the polymerization reactor with triethyl aluminum as a fiveweight percent isopentane solution so as to provide the activatedcatalyst in the reactor with an Al/Ti mol ratio of 30 to 40. Each of thepolymerization reactions was continuously conducted as describedpreviously.

Table II below lists the melt index, bulk density, particle size,percent fines and plasticizing time of the granular virgin resinproduced with the catalyst of the prior art (Example A) and the catalystproduced by the process of the present invention (Example B).

                  TABLE II                                                        ______________________________________                                        Comparison of Properties of Polyethylene Prepared With                        Catalyst of the Prior Art and the Present Invention                                             EXAMPLE                                                                       A     B                                                     ______________________________________                                        MI, dg/min          8.4     8.4                                               Density, g/cc       0.968   0.970                                             Bulk Density lb/ft.sup.3                                                                          30      25.6                                              Particle size, inches                                                                             0.022   0.026                                             Percent fines, <125 microns                                                                       10.4    3.8                                               Plasticizing time.sup.(1), sec.                                                                   17.5    12.0                                              ______________________________________                                         .sup.(1) A measure of time necessary to prepare molten polymer from the       resin in a standard injection molding machine.                           

The data of this table show that materials produced with the presentinvention contain less fines and exhibit lower plasticizing times.

COMPARATIVE EXAMPLES C AND D

A catalyst was prepared according to the procedure as found in U.S. Pat.No. 4,302,565 supra, as follows:

V. PREPARATION OF IMPREGNATED PRECURSOR COMPOSITION

The impregnated precursor composition was prepared by the method asdescribed in procedure Ia., supra.

VI. ACTIVATION PROCEDURE

The desired weights of impregnated precursor composition and activatorcompound are added to a mixing tank with sufficient amounts of anhydrousaliphatic hydrocarbon diluent such as isopentane to provide a slurrysystem.

The activator compound and precursor compound are used in such amountsas to provide a partially activated precursor composition which has anAl/Ti ratio of <0 to ≦10:1 and preferably of 4 to 8:1.

The contents of the slurry system are then thoroughly mixed at roomtemperature and at atmospheric pressure for about 1/4 to 1/2 hour. Theresulting slurry is then dried under a purge of dry inert gas such asnitrogen or argon, at atmospheric pressure and at a temperature of65°±10° C. to remove the hydrocarbon diluent. This process usuallyrequires about 3 to 5 hours. The resulting catalyst is in the form of apartially activated precursor composition which is impregnated withinthe pores of the silica. The material is a free flowing particulatematerial having the size and shape of the silica. It is not pyrophoricunless the aluminum alkyl content exceeds a loading of 10 weightpercent. It is stored under a dry inert gas such as nitrogen or argonprior to future use. It is now ready for use by being injected into, andfully activated within, the polymerization reactor.

When additional activator compound is fed to the polymerization reactorfor the purpose of completing the activation of the precursorcomposition, it is fed into the reactor as a dilute solution in ahydrocarbon solvent such as isopentane. These dilute solutions containsabout 5 to 30% by volume of the activator compound.

The activator compound is added to the polymerization reactor so as tomaintain the Al/Ti ratio in the reactor at a level of about ≧10 to 400:1and preferably of 15 to 60:1.

Ethylene was homopolymerized in each of Examples C and D with catalystfound as described by Procedure V and VI, above. The silica impregnatedprecursor composition (q calculated=6.5; q measured=6.5) contained 15(Example C) and 20 (Example D) percent by weight (percent loading) ofprecursor composition. The partially activated precursor composition(Al/Ti=5) was completely activated in the polymerization reactor withtriethyl aluminum so as to provide the activated catalyst in the reactorwith an Al/Ti mol ratio of 30 to 40. Each of the polymerizationreactions was conducted for >1 hour after equilibrium was reached andunder a pressure of about 300 psig, and temperature of 105° C.,according to the procedure as previously described.

Table III below lists percent loading of the precursor composition, H₂/C₂ mol ratio as well as melt index, melt flow ratio, density, residualtitanium, average particle size and bulk density of the granular virginresins made in these Examples.

                  TABLE III                                                       ______________________________________                                        Properties of Polyethylene Prepared With Catalysts                            of the Prior Art                                                                                EXAMPLE                                                                       C     D                                                     ______________________________________                                        Percent loading of the                                                        precursor composition                                                                             15      20                                                H.sub.2 /C.sub.2 ratio                                                                            0.358   0.381                                             MI, dg/min.         6.2     7.1                                               MFR                 26.7    25.8                                              Density, g/cc       0.969   0.969                                             Residual Ti, ppm    25      28                                                Average particle size, in.                                                                        0.019   0.02                                              Bulk density lbs/cu ft.                                                                           28.7    28.1                                              ______________________________________                                    

The data of Table III show that the polyethylene produced with thecatalysts of the prior art contains such higher residual titanium thanthe polyethylene produced with the catalyst of the present invention.

What is claimed is:
 1. A catalytic process for producing ethylenehomopolymers or copolymers with a Ti containing catalyst at aproductivity of ≧50,000 pounds of polymer per pound of Ti under apressure of <1000 psi in the gas phasesaid polymer being produced ingranular form and having a density of about ≧0.95 to ≦0.97 and a meltflow ratio of about ≧22 to ≦32 which comprises homopolymerizing ethyleneor copolymerizing ethylene with at least one C₃ to C₈ alpha olefin, at atemperature of about 30° to 115° C. by contacting the monomer charge inthe gas phase reaction zone, with particles of a catalyst systemcomprising a precursor composition impregnated in a porous support andwhen so impregnated having the formula:

    Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q

wherein R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, orCOR' wherein R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbonradical, X is selected from the group consisting of Cl, Br, I, ormixtures thereof, ED is an electron donor compound, m is ≧0.5 to ≦56, nis 0, 1 or 2, p is ≧2 to ≦116 and q=1.5 m+2, ED is a liquid organicelectron donor compound in which said precursor composition and the Tiand Mg component thereof are soluble and which is selected from thegroup consisting of alkyl esters of aliphatic and aromatic carboxylicacids, aliphatic ethers, cyclic ethers and aliphatic ketones, saidimpregnated precursor composition being activated in said reaction zonewith >10 to 400 mols of activator compound per mol of Ti in saidprecursor composition, said activator compound having the formula

    AlR.sub.3

wherein the R's are the same or different, and are C₁ to C₁₄ saturatedhydrocarbon radicals.
 2. A process as in claim 1 in which ethylenehomopolymer is produced.
 3. A process as in claim 2 in which saidmagnesium compound comprises MgCl₂.
 4. A process as in claim 2 in whichsaid electron donor compound comprises at least one ether.
 5. A processas in claim 4 in which said electron donor compound comprisestetrahydrofuran.
 6. A process as in claim 2 in which said titaniumcompound comprises TiCl₄.
 7. A process as in claim 2 wherein the carriermaterial comprises silica.
 8. A process as in claim 7 wherein the silicais treated with at least one activator compound of the formula

    AlR.sub.3

wherein the R's are the same or different, and are C₁ to C₁₄ saturatedhydrocarbon radicals.
 9. A process as in claim 1 which is conducted in afluid bed process.
 10. A process as in claim 9 which is conducted undera mass gas flow rate of about 1.5 to 10 times G_(mf).